722
Oct., 1909
THE JOURNAL OF INDUSTRIAL A.VD EI‘VGI-VEERING CHEMISTRY.
in the arc light pencils. The oxides reduced by the above-described process to the metallic state were then again oxidized in the arc to their previous condition. These processes of oxidation supplied the pencils with the heat necessary for the ionization that caused the selective radiation and luminosity of the arc. This storing u p of energy is the principal distinctive feature differentiating the metallic rutile pencil from the mere conglomeration of the oxygen compounds of iron with oxygen compounds of titanium known under the name of magnetite arc light pencils now on the market. Consequently the author considers himself justified in claiming that his arc light pencil prepared of a mixture of oxygen compounds of iron and titanium, subjected to a process of reduction, are actually ferrotitanium pencils, inasmuch as they contain the metallic titanium and metallic iron, conglomerated and intermingled with each other in one solid cylindrical body. I n order to verify the above formulated conclusion, another electrode, made as above described, was analyzed with the following results: Per cent. Metallic iron. . . . . . . . . . . . . . . . . . . . 6 4 . 8 9 Oxides of titanium.. . . . . . . . . . . . . . 2 6 . 6 9 (by diff.) 1.99 Silica. Metallic titanium. . . . . . . . . . . . . . . . 1 . 8 2 1 .08 rllumina ........................ 1 .os Magnesia.. 0 .so Lime. ..........................
..........................
...
0.75 0.50
0.32 Carbon ......................... 0 .os Sulphur. Trace Phospho . . . . . . . . . . . . . . . . None Chromiu Metallic titanium soluble in hydrochloric acid.. . . . . . . . . . . . . . . . . . 1.86
This pencil contains 3.60 per cent. of a 50 per cent. ferro-titanium, assuming that the alloy of iron and titanium exists here in the proportion of one part of metallic titanium to one part of nietallic iron. The reason for a lower percentage of metallic titanium in this pencil than that found in the pencil reported a year ago, is that in the former pencils there was present a total of about 45 per cent. of titanium calculated as titanic acid, whereas in this pencil there is present a total of only 29 per cent. of titanium calculated as titanic acid. The presence of iron in metallic state is demonstrated beyond doubt and the fact that titanium was obtained in solution by treatment with hydrochloric acid shows, according to recognized authorities
in chemistry, present .
that
metallic
titanium
is
also
REPORT O F LIFE TESTS OF IMPROVED TITANIUM ELECTRODES. DURAT I O N OF EACH TEST100 HOURS.
Pencil E-5/8”
diam. X 8” long:
1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 ............................... 3 ...............................
57.14 43.23 43.96
-
Average hours per inch. . . . . . . . . . . . 4 8 . 1 1 Pencil D r 9 / 1 6 ” diam. X 8” long. 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 ............................... 3 ...............................
53.33 44.44 44.83
Average hours per inch. . . . . . . . . . . . 4 7 . 5 3 Pencil E3-9/32” diam. X 8” long. 1
...............................
50.00 30.76 37.18
2 ............................... 3 ...............................
Average hours per inch.. . . . . . . . . . . . . 3 9 . 3 1 Pencil E3-5/8” diam. X 8“ long. 1 ............................... 2 ............................... 3 ...............................
57.14 43.23 43.96
Average hours per inch.. . .
Comparative data as to the life of the improved titanium arc light electrodes and carbon electrodes (at their respective nor.ma1 current density per square mm.) : Cm. per one hour. Life Life Life Life Life Life Life
of of of of of of of
the the the the the the the
D titanium pencil 9/16 in d . . . . . . . . . . averaged cored carbon , , . solid carbon.. . . . . . . . . . . . . enclosed,carbon.. . . . . . . . . . . . . . . . . . . . flaming carbon. ..................... Bremer type carbon.. . . . . . . . . . . . . . . . Blonde1 type carbon. . . . . . . . . . . . . . . . .
.
0.075
0.152 3.00 4 .OO 2 .OO
The increased life of the titanium pencil in hours per inch in comparison with the following carbons, is : Cored carbons. . . . . . . . . . . . . . . . . . . . 17.35 times. ...
19.33
Enclosed carbons. . . . . . . . . . . . . . . . . 2 . 0 3 Flaming carbons. . . . . . . . . . . . . . . . . . 40 .OO Bremer type carbons. . . . . . . . . . . . . . 5 3 . 3 3 Blonde1 type carbons.. . . . . . . . . . . . . 2 6 . 6 7
‘‘ ‘‘ “ “
*‘
Comparative specific resistivity of the titanium arc light electrode and various carbon electrodes ( I ni. long, I mm.2 in diameter) : Solid carbons. Solid carbons. Solid carbons. Average
Brand Conradty C. . . . . . . . . . . . . Brand Henrion (Nancy). . . . . . . . Brand Plania.. ................
..................................
Cored carbons. Cored carbons.
Average ..................................
72 .O 81 . O
76.5
.
Brand Plania, solid.. , Brand Eos, solid. . . . . .
Average ..................................
69 . O 79 . O 72.3
Brand Siemence A . . . . . . . . . . . . Brand Plania.. . . . . . . . . . . . . . . .
Enclosed lamp carbons. Enclosed lamp carbons.
Ohms. 69 . O
81 .O 89 . O 85.0
ROBERTSON ON DETERMINI-VG CASEIN I N AIILK. Bremer type carbons. Brand Plania, white.. ... Bremer type carbons. Brand Plania, with nickel-plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bremer type carbons. Brand Plania Rosa.. . . . . Bremer type carbons. Brand, Plania, yellow.. . . Bremer type carbons. Brand Siemence, white.. Bremer type carbons. Brand Siemence, yellow.. Bremer type carbons. Brand Siemence, yellow, with copper-plating. ....................... Bremer type carbons. Brand Siemence Conradty Noris, yellow, with copper-plating.. . . Same, with wire in the core.. .. ;. . . . . . . . . . . . . . Siemence, yellow, with metallic wire in the core. . Average.
.................................
Ohms. 84 . O 58 . O 88 . O 87 . O 93 . O 106.0 29.3 60.5 81 .O 39.0 72.58
The resistivity of the titanium pencil is 2 . 0 2 ohms. Consequently : The resistivity of the average solid carbon pencil is 36 times. The resistivity of the average cored carbon pencil is 38.2 j times. The resistivity of the average enclosed carbon pencil is 42, j times. The resistivity of the average Bremer type carbon is 36.2 times that of the titanium pencil. [FROM THE RCDOLPH SPRECKELS PHYSIOLOGICAL LABORATORY OF
THE
USIVERSITYOF CALIFORNIA]
A R A P I D METHOD O F DETERMINING THE PERCENTAGE O F CASEIN IN MILK. BY T BRAILSFORD ROBERTSON Received May 10, 1909
In a recent paper‘ I h a r e shown that the difference betveen the refractive indices of two solutions of a caseinate, which differ only in their casein-content, is proportional to the difference between the percentages of casein which they contain; in other words, that n-- n, = a X c, where n is the observed refractive index of the solution, c is the percentage of casein which it contains, n, is a constant, the value of which depends upon the concentration and nature of the alkaline (or acid) solution employed as solvent, and LI is a constant numerically equal to the change in the refractive index of the solvent which is brought about by the addition to IOO cc. of I gram of casein. I have also shown that by means of the above formula the concentration of casein in a solution can be very accurately determined, the deviations from accuracy rarely exceeding 2 per cent. of the quantity of casein contained in IOO cc of the solution (provided that quantity exceeds o j gram) and that the change in the refractive index of a given volume of a solution of a base which is brought 1T
(1909).
Brailsford Robertson
Journ
of
Physical C h e m , 13, 469
723
about by the introduction of a given weight of casein is independent of the concentration of the base and of the nature of the base; if the volume be IOO cc. and the weight of casein I gram, the change in the refractive index is 0.00152. I t occurred to me that these facts might be applied to the determination of the percentage of casein contained in fluids such as milk.‘ The procedure of the determination was as follows: Fifty cc. of fresh, unskimmed milk were diluted to 250 cc. and 75 cc. of N / I Oacetic acid (made up by diluting I O cc. of glacial acetic acid to 1750 cc.) were slowly added, the mixture being continuously and rapidly stirred during the addition. The precipitate was then allowed to settle and the supernatant fluid was poured through a I j cm. s. & No. 589 “white band” paper. The precipitate was then washed by decantation with distilled water several times, the washings, and, subsequently, the precipitate being transferred to the same filter. The filter and precipitate were then allowed to drain for about I hour and were then transferred to a dry beaker and IOO cc. (accurately measured) of N / I O NaOH were added and the filter and precipitate were macerated (by the aid of a stirring rod protected a t the tip by rubber) until the filter paper was transformed into a fine pulp and the casein was completely dissolved. As the casein particles are of a different color to the particles of paper, the point of complete solution can be readily determined; complete solution of the amounts dealt with in this determination is usually attained within ten minutes. The mixture mas then filtered2 and the refractive index of the filtrate determined, by means of a Pulfrich refractometer reading accurately to within I ’ of the angle of total reflection, if possible a t 20’ C. Since n for N l I O NaOH is I . 33444 (at zoo C.),3 the results are calculated as follows: Grams casein in 50 cc. milk = n - 1 33444, 0.00152 where n is the refractive index of the final solution, obtained as described above. An obvious source of error is the water associated with the precipitate and filter paper when they are transferred to the Nj1o NaOH. As the SUCceeding determinations show, however, with the
s.
’
~
~
1 Since writing the above, I have found that Reiss (Arch. f . Ex$er. Palhol. u n d Pharm., 51, 18 (19C3); Bezfr. z. chem. Physiol. und Pathol., 4 , 150 ( 1 9 0 4 ) ) has previously employed the refractive indices of bodyfluids as a measure of their protein-content. 2 This filtration can be omitted provided the solution be allowed to stand for a sufficient time so that the particles of paper settle to the bottom of the beaker. a Cf. the paper cited above
724
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING C H E M I S T R Y .
amounts of casein likely to be obtained from 50 cc. of milk, and provided the precipitate is allowed to drain for a sufficient time this error is, for all practical purposes, negligible. It could, of course, be eliminated, if desired by diluting the final solution, before filtration, to an accurately measured volume with N,’Io NaOH; in that case i t would be advisable to start with 100 cc. of milk instead of 50 cc., completely dissolve the precipitate in 100 cc. of N / I O NaOH and then make up the volume of the mixture to 2 0 0 cc. by the addition of N / I O NaOH. The slight dilution of the sodium hjdroxide caused by this procedure does not affect the accuracy of the determination, since the refractive index of a dilute sodium hydrate solution yaries very much less with its concentration than that of a solution of casein of the concentrations employed above. For comparison, determinations were carried out by the official methodl as follows: Twenty cc. 0: fresh unskimmed milk; were diluted to IOO cc. and 30 cc. of N / I O acetic acid were s’owly added, the mixture being continuously and rapidly stirred during the addition. The precipitate tyas then allowed to settle and the supernatant fluid was poured through a 1 5 cm. s. & s. No. 589 “white band” paper. The precipitate was then washed by decantation with distilled water several times, the washings, and, subsequently, the precipitate being transferred to the same paper. The filter and precipitate were then digested with 2 0 cc. of H,SO,, to which a trace of metallic mercury had been added, as in the ordinary Kjeldahl method for the determination of nitrogen, and the process of determining the nitrogen was completed by the official Kjeldahl method. The number of grams of casein in the 20 cc. of milk was estimated by multiplying the number of grams of nitrogen thus determined by 6 . 2 5 . Four determinations b y the new method yielded the following results : Grams casein in 100 cc. milk. a................................ 2.84 . . . . . . . . . . . . 2.84 . . . . . . . . . . . . 2.84 . . . . . . . . . . . . . . . 2.84 Average ........................
2.84
Four determinations by the official method, 1 U.S . Department of Agriculture, Division of Chemistry, Bulletin 4 6 , Revised Edition (18991, p . 55. The details of the precipitation were slightly modified and the quantity of milk employed in the determination was double that recommended b y the Association of Official Agricultural Chemists.
Oct., 1909
using the same milk,, yielded the following re~, sults : Grams casein in 100 CC. milk.
.. a . .. . . . . . . . . . . . . b............
.......
d ....................
2.69
-
The agreement is sufficiently satisfactory. The factor 6 . 2 5 by which the nitrogen is multiplied to obtain the equivalent in casein is calculated on the assumption that the percentage of nitrogen in casein is 16. If, however, we take 15.65 as the true percentage of nitrogen in casein, which, according to the results of Hammersten,’ Lehmann and Hempel,? and Ellenberger,3 would appear to be the more accurate figure, then the factor by which nitrogen is multiplied becomes 6 . 4 and the agreement between the official and the new methods is even more satisfactory, the above four determinations by the official method yielding the results: ......................
Grams casein in 100 cc. milk. 2.75
............... Average.
2.75
__
............
In order to further test the accuracy of the method, weighed amounts of casein were dissolved each in IOO cc. of N l 5 o NaOH and were precipitated, with constant stirring, by the addition of j o cc. of N / I O acetic acid. The casein employed in these experiments was the c. p. product manufactured b y Eimer & Amend and further purified by trituration with large volumes of distilled water alcohol (absolute) and ether (ueber natrium dist.) ; i t was dried for 24 hours a t 36’. The properties of the product thus obtained have been fully described by me in a previous paper;4 i t gives every indication of being a pure product, being insoluble in distilled water (save in traces which adhere to the undissolved particles) and completely precipitated by acetic acid. I t neutralizes to phenolphthalein exactly the quantity of base determined by Laqueur and Sackur and by \‘an Slyke and H a r t ; j i t is free from appreciable water. The first 1 0 . Hammersten, Zeitschu. f . Physiol. Chem., 7 , 227 (1883); 9, 273 (1885). 2 W. Hemnel, Arch. I. d . ees. Physiol., 66, 558 (1894). . , Ellenberger, Arch. f . Anat. und Physiol., Physiol. Abt. Suppl., p. 313 (1902). 4 T.Brailsford Robertson. Journ. of Biol. Chem., 2 , 317 (1907). Laqueur and Sackur. Beitr. 2. Chem. Physicl. u. Path., 3 , 193 (1902). Van Slyke and Hart, Amer. Chem. Journ., 33, 461 (1905).
